Modified traveling wave tube



May 7, 1968 K. GAROFF MODIFIER TRAVELING WAVE TUBE Filed May 6, 1963 ELECT COOLANT BERYLLIA INVENTOR, KENTQN GAROFF Q MM M W ATTORNEYS United States Patent 3,382,399 MODIFIED TRAVELING WAVE TUBE Kenton Garotf, Little Silver, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed May 6, 1965, Ser. No. 453,846 1 Claim. (Cl. 3153.5)

ABSTRACT OF THE DISCLOSURE A traveling wave tube including a transmission circuit which comprises an evacuated annular cylinder having an outer metallic surface and an inner surface made of beryllia upon which is deposited a slow-wave propagating structure. An annular electron beam passes through the evacuated cylinder and interacts with the electromagnetic wave propagated along the slow-wave circuit, and a liquid coolant is passed through the center of the beryllia cylinder and in contact with the beryllia surface. To provide an axial magnetic field, a permanent magnet is axially aligned within the cylinder.

This invention relates to traveling wave tubes and more particularly to traveling wave tubes utilizing pre-formed or printed wave propagating structures.

Traveling wave tubes generally consist of a slow-wave propagating structure through or along which an electron beam is directed so that an interaction between this electron beam and a component of the electromagnetic wave on the structure may occur. Conventionally, such wave propagating structures usually consist of a helix supported by rods or wedges. Recently, however, it has been found that such helical structures could be produced by means of a photo deposition process wherein the slow-wave helical structure is deposited on a cylinder made of beryllia or other suitable ceramic material. For etlicient operation, the inside of the ceramicycylinder was evacuated to provide a high vacuum. Although helical wave propagating structures made in accordance with the photo deposition process were found to have greater stability and linearity than conventional helical propagating structures and could also be produced cheaply in large quantities with the same uniform characteristics, certain limitations and disadvantages were inherent in such structures. For example, a helical propagating structure made by the deposition process usually required a non-propagating helix within the ceramic cylinder to provide a leakage path therefrom for any electric charges resulting from the passage of the electron beam within and in close proximity to the ceramic cylinder. The requirement of such a non-propagating helix complicates the construction of the traveling wave tube and also increases the cost thereof. Also, the presence of the ceramic cylinder concentrates fields through the ceramic or very close to it, thereby making it difficult to exchange energy between the electron beam and the photo deposited helical structure. The concentration of such fields becomes greater at higher frequencies thus setting upper limits where efficiency degenerates very heavily and losses in the ceramic becomes too great.

It is an object of the present invention to provide a traveling wave tube wherein the above limitations are overcome.

It is another object of the present invention to provide an improved traveling wave tube adapted to operate at relatively high frequencies with high interaction efficiency.

In accordance with the present invention, there is provided a traveling wave tube which includes a transmission circuit comprising an evacuated annular cylinder having 3,382,399 Patented May 7, 1968 an outer metallic surface and an inner ceramic surface. The ceramic surface has deposited thereon a helical slow wave propagating structure or any other suitable slowwave structure. Included further is an annular electron beam which passes through the evacuated annular cylinder and interacts with the electromagnetic wave propagated along the helix.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing which illustrates an embodiment of. my invention.

Referring now to the drawing, there is shown at 10 a traveling wave tube having at one end thereof an electron gun 12 which serves as the source of an annular cylindricalelectron beam. The electron gun 12 is of a design well known in the art and the electron emissive annular cathode is shown at 14. At the opposite end of the tube 10 there is provided a collector electrode 16 which is in target relation with the cathode 14 to collect the spent electrons. The axially aligned propagating wave structure comprises an annular cylinder 18 having an outer metallic cylindrical surface 20 and an inner cylindrical surface 22 made of a suitable ceramic such as beryllia which contains the helical slow wave structure 24 or any other well known slow-wave circuit. As hereinabove mentioned, the helical slow-wave structure 24 is deposited on the ceramic surface by means of a photo deposition process well known in the art. The annular cylinder 18 is terminated at one end by the collector electrode 16 which is hermetically sealed to both the inner and outer surfaces of annular cylinder 18. The other end of the annular cylinder 18 is terminated by an annular metallic cover 28 which is also hermetically sealed to both the outer and inner surfaces of annular cylinder 18. The annular cylinder 18 is evacuated to provide a high vacuum. As shown, the annular beam derived from cathode 14 is passed through the evacuated annular space of cylinder 18 to the collector target electrode 16. A permanent magnet as at 30, may be centrally positioned along the axis of the cylinder 18 to provide the necessary magnetic field to focus the annular electron beam as it passes through the evacuated annular space of the cylinder 18. It is to be understood of course that the permanent magnet 30 is shaped to provide a uniform field. If desired, an external magnetic field surrounding the outer metallic surface 20 may be provided in the conventional manner. Cooling of the helix 24 is accomplished by passing water or other suitable cooling liquid through the center of the cylinder 18 so that the cooling liquid is in contact with the beryllia surface 22. Suitable coupling leads, as at 32 and 34 are brazed to the ends of the deposited helical structure 24 to provide input andoutput electromagnetic wave coupling leads into and out of the deposited helical structure 24.

In operation, the electromagnetic wave energy is propagated along the helical structure 24 by any suitable means well known in the art. The required velocity of the annular electron beam may be controlled by suitable D.C. potentials which have been eliminated for purposes of clarity. The hollow beam generated at the cathode interacts with the longitudinal fields between adjacent turns of the helical structure 24 and the spent beam is collected by the target electrode 16.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a traveling wave tube utilizing a wave transmission circuit for propagating electromagnetic waves in field coupling relation with an electron stream, the combination including a transmission circuit comprising an evacuated annular cylinder having an outer metallic surface and an inner surface comprised of beryllia, said beryllia surface having deposited thereon a helical slow-wave structure, an annular electron beam passing through said evacuated cylinder and interacting with the electromagnetic wave propagated along said helix, a liquid coolant passing through the center of said cylinder and in contact with said beryllia surface, and a permanent magnet axially aligned within said cylinder for providing a magnetic field for focusing said annular electron beam.

4 References Cited UNITED STATES PATENTS ELI LIEBERMAN, Primary Examiner. O HERMAN KARL SAALBACH, Examiner.

S. CHATMON, 111., Assistant Examiner. 

